Acrylonitrile polymer composition stabilized with phenolphthalein and an inorganic acid and method of making same



United States Patent" ACRYLONITRILE POLYMER COMPDSITION STA- BILIZED WITH PHENOLPHTHALEIN AND AN gg IlEGANIC ACID AND METHOD OF MAKING Richard R. Holmes, Bethesda, Md., and Lloyd T. Jenkins,

Decatur, Ala., assignors to The .Chemstrand Corporation, Decatur, Ala., a corporation of Delaware No Drawing. Application May 23, 1956 i Serial No. 586,671

16 Claims. (Cl. zen-32.6

This invention relates to the stabilization of acrylonitrile polymers and blends thereof. More particularly,

it relates to the stabilization of acrylonitrile polymers and blends thereof which have a tendency to develop color upon standing or application of heat. I

i The term polymer, as employed in the instant de scription and claims, is intended to include homopolymers, copolymers, and blends thereof, said polymers, containing at least 80 percent by weight of polymerized or copolymerized acrylonitrile, in the polymer molecule.

Acrylonitrile polymers containing 80 percent or more of acrylonitrile are generally insoluble infthe more com- Inon solvents. In those instances where suitable solvents have been found, in order to effect solution, the application of heat is usually necessary. Where heat is employed to effect solutions, from whichjshaped articles areto be formed, a tan to dark brown color frequently develops in the solutions and therefore is carried over. into the product formed therefrom. This color also develops in solutions upon standing for prolonged periods .oftime.

The mechanism which causes color formation has not been definitely ascertained, although a variety of reasons ble standards and therefore, has -been the source of concern, particularlyin commercial operations where such types of polymers or copolymers are employed.

Accordingly, it is an object of the present invention to prevent undesirable color formation in acrylonitrile polymer compositions.

Patented Mar. 17, 1959 "ice 2 3 plished by dissolving the polymer of acrylonitrile in a suitable solvent therefor and preventing or minimizing color formationby the presence in the solution as an inhibitingagent, a combined reagent comprising phenolphthalein and an inorganic acid having an, ionization constant'greater than 1X 10-. n

The components of the inhibiting agent may be employed in equal or unequal amounts, any one constituent being present in a range of from 9910 1 percent in a two component system. The total amount of inhibiting agent may be employed in a range of about 0.3 to 15 percent, based on the total polymer weight. 'However, it is preferred that the inhibiting agent of the instant invention be present in a small amount compared to the amount of polymer dissolved. Thus, although the amount is not critical, it is preferred that the inhibiting agent be present in the amount of about 0.3 to 3 percent, based on the total weight of the polymers. The inhibiting agent may be added to the solvents before or after the polymer 1s dissolved therein. The inhibiting agent permits exposure to high temperatures for prolonged standing periods without the development of the objectionable color which usually results in such solutions. The compositions of the instant invention maybe prepared in a varying temperature range. For example, the compositions of the instant invention may be prepared by mixing the polymer, a suitable solvent and the inhibiting agent at any temperature or heating the mixture to a temperature up to the boiling point of the solvent.

Among the acids which may be employed in practising theinstant invention are sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, etc.

, Among the solvents which may be used in practising the instant invention are N,N-dimethylformamide, N,N dimethyiacetamide, aqueous zinc chloride, sulfuric acid, aqueous nitric acid, aqueous sodium thiocyanate, ethylene carbonate, sulfolane, nitromethane,,etc.

The polymeric materials, which may be employed in the practice of the present invention, are polyacrylonitrile, cop olymers, including binary and ternary polymers containing at least 80 percent by weight of acrylonitrile in the polymer molecule, or a blend comprising polyacrylonitrile or copolymers comprising acrylonitrile with from 2 to percentof another polymeric material, the blend'having an, overall polymerized acrylonitrile, content of at leastSO percent by weight. While the preferred polymersemployed in the instant invention are those contain- Another object is to minimize color formation when solutions of the acrylonitrile polymers are permitted to stand for a prolonged period of time or upon application of heat.

It is also an object of the invention to prevent color formation in acrylonitrile polymers at elevated-tempera- Other objects and advantages willbe apparent from a consideration of the description of the. invention .which follows hereafter.

In general, the objects of the invention are accoming at; least .80 percent. of acrylonitrile, vgenerally recognized aggihe fiber-forming acrylonitrile polymers, it will be understood that the invention is likewise applicable to polymers containing less thanSO percent acrylonitrile and the).same stability is realized with the inhibiting agents defined herein. The acrylonitrile polymers containing less than percent acrylonitrile are useful in forming films, coating compositions, molding operations, lacquers, etc., in all of which applications the alleviation of undesirable coloris extremely important.

For example, the polymer may be a copolymer of from 80 to 98 percent acrylonitrile and from 2 to 20 percent of another monomer containing the C=C linkage and copolymerizable with acrylonitrile. Suitable monoolefinic monomers include acrylic, alpha-chloroacrylic and methacrylic acids; the acrylates, such as methylmethacrylate, ethylmethacrylate, butylrnethacrylate, methoxymethyl methacrylate, beta-chloroethyl methacrylate, and the corresponding esters of-acrylic and alphachloroacrylic acids; vinyl chloride, vinyl fluoride, vinyl bromide, vinylidene chloride, l-chloro-l-bromoethylene; methacrylonitrile; acrylamide and methacrylamide; alphachloroacrylamide, or monoalkyl substitution products thereof; methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinyl chloroacetate, vinyl propionate, and vinyl stearate; N-vinylimides, such as N-vinylphthalimide and N-vinylsuccinimide; methylene malonic esters; itaconic acid anditaconic ester; N-vinylcarbazole; vinyl ,furane; alkyl' vinyl esters; 'vinylzsulfonic acid; ethylene alpha, beta-dicarboxyli'c acids '01 their 'anhydrides or derivatives, 'such' 'as diethylcitraconate, diethylmesaconate, styrene, vinyl naphthalene; vinyl-substituted tertiary heterocyclic amines, such as the vinylpyridines and alkylsubstituted vinylpyridines, for example, i2-vinylpyridine,

4-vinylpyridine, .2-methyl 5-vinylpyridine, etc.;' l-vinyl- 'imidazole and alkyl-substituted 'l-vinylimidazoles, such as 2-, 4-, or .S-methyl-l-vinylimidazole, and other C=C containing polymerizable materials.

The polymer may be a ternary interpolyrn'er, for example, products obtained by the interpolymerization of acrylonitrile and two'or more of any of the monomers, other than acrylonitrile, enumerated above. Morespecifically, and preferably, the ternary polymer comprises acrylonitrile, methacrylonitrile, and 2-vinylpyridine.- The ternary polymers preferably contain from"80 to 97 percent of acrylonitrile,'from 1 to percent of 'a vinylpyridineor a l-vinylimida'zole, and from 1 to 18 percent of another substance, such as metha'c'rylonitrile or vinyl chloride. a The polymer may also bea blend of p'olyacrylonitrile or of a binary interpolymer of from '80 to 99 percent acrylonitrile and from 1 to 20 percent of at least' one other C=C containing substance withfrom 2 to 50 percent of the weight of the blend'of afcopolymer of from 10 to 70 percent of acrylonitrile'and from "30 to 90 percent of at least one other ChC containing poly- 'merizable"monomer. Preferably, whenthe polymeric material comprises a blend, it will beat blendo'f a copolymer of 90to 98 percent acrylonitrile and from 2 to 10 percent of another mono-'olefinic monomer, suchas vinyl acetate, which is not receptive'to 'dyestufflwith a sufficient amount of a copolymer 'of'from 10 to 7'0 percent of acrylonitrile and from '30 to '90p'ercent of a vinyl-substituted tertiary heterocyclic'aminasuch as vinylpyridine or l-vinylimidazole, to give a dyeable blend :having an overall vinyl-substituted tertiary heterocyc'lic amineContent of from 2 to 10 percent, based on the weight *dfqthe 'blend.

The polymers,useful'in the'practice of the'present invention, may be prepared by any conventional polymerization procedure, such as mass polymerization methods, solution polymerization methods, or aqueous emulsion procedures. However, the preferred practice utilizes suspension polymerization wherein the polymer isprepared in finely divided form for immediate use 'in the fiber fabrication operations. The preferred suspension polymerization may utilize batch procedures, wherein monomers are chargedwith an aqueous medium containingthe necessary catalyst and dispersing agents. A more 'desirable method involves the'semi-continuous procedurein which the polymerization reactor containing the aqueous medium is charged with'lthe desired monomers and the continuous withdrawal of polymer may'also be"empl'oyed,'

The polymerization is catalyzed byrn'eans of any'waten "soluble'peroxy compound,'fortexamp'le thejpotassiumam' monium and other water soluble salts of iperoxy -"acids,

:sodium peroxide, hydrogen peroxide, "sodium ipe-rborate,

the sodium salts :of other peroxy "acids, and any other water-soluble "compound containing a peroxy group (-O--O-- A wide *variation in thequantitv-p'f per 'oxy compound "is possible. 'For examplej'from 011 to 3.0

percent by weight of the 'polymeriz-able monomermay be used. The catalyst may be charged at the outset of .the reaction, .or it maybe added continuously or in increments throughout the reaction for the purpose of maintaining a more uniform concentration of catalyst in the reaction mass; The latter method is preferred because it tends to make ,the resultant polymer more uniform in it chemical and physical properties.

Although the uniform distribution of the reactants throughout the reaction mass can be achieved by vigorous agitation, it is generally desirable to promote the uniform distribution of reagents by using inert wetting agents, or emulsion stabilizers. Suitable reagents for this purpose are .the water-soluble salts .of fatty acids, such as sodium oleateand potassium stearate, mixtures of water-soluble fatty acid salts, such as common soaps prepared by the saponification of animal and vegetable oils, the amino soaps, such as salts of triethanolamine and dodecylmethylamin'e, salts of rosin acids and mixtures thereof, the water-soluble salts of half esters of sulfuric acid and long chain aliphatic alcohols, sulfonated hydrocarbons, such as alkyl aryl sulfonates, and any other of a wide variety of wetting agents, which are in general organic compounds containing both hydrophobic and hydrophilic radicals. The quantity of emulsifying agents will depend upon the particular agents selected, the ratio of monomer to be used, and theconditions of polymerization. In general, however, from 0.01 to 1.0 percent by weight of the monomers may be employed.

The emulsion polymerizations are preferably conducted in glass or glass-lined vessels which are provided with a means for agitating the contents. Generally, rotary stirring devices are the most effective means of insuring the intimate contact of'the reagents, but other methods may be successfully employed, for example by rocking or tumbling the reactors. "Theflpolymeriz'ation equipment generally used is conventional in the art and the adaptation of a particular-type of apparatus to the reaction contemplated is within the ,province of one skilled in the art. The articles manufacture'd'therefrom may be produced by well-known conventional methods, for example, the wet-spinning, dry-spinning and melt-spinning methods for producing fibers.

The following examples are illustrative rather than "limitative and all parts, proportions and percentages are by weight unless otherwise specified.

EXAMRLE 'I 755 grams are polymer blend of 88 percent "of a "copolymer"containing"94;percent of acrylonitrile and 6 percent dfwinylacetate'and l2 percent-"of 'a copolymer of 50 percent "of 'acrylonitrile,'and 50 percent of ZmethyI-S- vinyhpyridine were addedto 4'5 milliliters of .N',N-dime'thylacetami'decontaining approximately 0.05 gram of Table l Inhibitor Percentage" Purity Used 755 grams of a 'copolymer -containing94 percent :of acrylonitrile and .6 percent of vinyl acetate were .ia'dded to '4"S*milliliters of N',N- dimethylac'etamide containing approximately 0.05 gram of titanium dioxide. Thelm'ixture was stirred andheated for '35 minu,tes at 70 .C. It was then quickly -cooled' 'to room temperature and the color measured. This sample was used as a control,

Control- .l Phenolphthalein and Sulfuric Acid 2 The purity is set forth below. Subsequently, a like sample was prepared but with 0.150 gram of an inhibiting agent containing 0.075 gram each of phenolphthalein and sulfuric acid. The purity is set forth below.

T able ll Inhibitor Percentage Purity Used EXAMPLE III 7.5 grams of an acrylonitrile homopolymer were added to 45 milliliters of N,N-dimethylacetamide containing approximately 0.05 gram of titanium dioxide. The mixture was stirred and heated for 45 minutes at 70 C. It was then quickly cooled to room temperature and the color measured. This sample was used as a control. The purity of the control sample is set forth below. Subsequently, a like sample was prepared but with 0.150 gram of an inhibiting agent containing 0.075 gram each of phenolphthalein and sulfuric acid. The purity is set forth below.

Table III Inhibitor Percentage Purity Used Control Phenolphthalein and Sulfuric Acid 2 The tests for color indicative of approaching whiteness used throughout the examples consist of measurements of purity as calculated from the tristimulus values determined on a General Electric spectrophotometer by the methods recommended by the Standard Observer and Coordinate System of the International Commission on Illumination, as fully set forth in the Handbook of Colorimetry published by The Technology Press, Massachusetts Institute of Technology in 1936.

The compositions of the instant invention present many advantages. For example, products formed from the polymer solutions of the instant invention are free of objectionable color and therefore of greater commercial value. In preparing the polymer solutions, heat may be applied without the danger of color formation and the solutions, if necessary, may stand for prolonged periods and remain free of color. The inhibiting agents are readily available and inexpensive. Therefore, no great increase in production cost is necessary. The compositions containing the inhibitors may be prepared without going through detailed and elaborate procedures that necessitate expensive changes in the design of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparently widely different embodiments of this invention can be made without departing from the spirit and scope thereof. Accordingly, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a polymer containing at least 80 percent of polymerized acrylonitrile and up to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith, a solvent therefor, and an inhibiting agent containing substantially equal proportions by weight of phenolphthalein and an inorganic acid having an ionization constant greater than 1 10"*.

2. A new composition of matter as defined in claim 1 wherein the polymer is a copolymer containing from 80 to 98 percent of acrylonitrile and from 2 to 20 percent of anotherpolymerizable mono-olefinic monomer copolymerizable therewith.

3. A new composition of matter as defined in claim 1 wherein the polymer is a blend of to 99 percent of (A) a copolymer containing to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of Z-methyl-S-vinyl pyridine.

4. A new composition of matter as defined in claim 1 whereinthe polymer is polyacrylonitrile.

. 5. A new composition of matter as defined in claim 1 wherein the solvent is N,N-dimethylformamide.

6. A new, composition of matter as defined in claim 1 wherein the solvent is N,N-dimethylacetamide.

7. A new composition of matter comprising a polymer blend of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of another polymerizable mono-olefinic monomer and (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of a vinyl substituted tertiary heterocy'clic amine, said blend having an overall vinyl substituted tertiary heterocyclic amine content of from 2 to 10 percent based on the weight of the blend, a solvent therefor, and an inhibiting agent containing substantially equal proportions by weight of phenolphthalein and an inorganic acid having an ionization constant greater than 1 10 8. A new composition of matter comprising a copolymer containing 80 to 98 percent of acrylonitrile and 2 to 20 percent of vinyl acetate, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of an inhibiting agent, said inhibiting agent containing substantially equal proportions by weight of phenolphthalein and sulfuric acid.

9. A new composition of matter comprising a polymer blend of 80 to 99 percent of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of Z-methyl-S-vinyl pyridine, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of an inhibiting agent, said inhibiting agent containing substantially equal proportions by weight of phenolphthalein and sulfuric acid.

10. A new composition of matter comprising: a polymer containing at least 80 percent of poyymerized acrylonitrile and up to 20 percent of another polymerizable monoolefinic monomer copolymerizable therewith, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of an inhibiting agent, said inhibiting agent containing substantially equal proportions by weight of phenolphthalein and sulfuric acid.

11. A method for preparing a new composition of matter comprising mixing a polymer containing at least 80 percent of polymerized acrylonitrile and up to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith, a solvent therefor, and an inhibiting agent containing substantially equal proportions by weight of phenolphthalein and an inorganic acid having an ionization constant greater than 1 10- and heating the mixture to form a homogeneous solution.

12. The method as defined in claim 11 wherein the polymer is a copolymer containing from 80 to 98 percent of acrylonitrile and from 2 to 20 percent of another polymerizable mono-olefinic monomer copolymerizable therewith.

13. The method as defined in claim 11 wherein the polymer is a blend of 80 to 99 percent of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of 2-methyl-5-vinyl pyridine.

14. The method as defined in claim 11 wherein the polymer is polyacrylonitrile.

15. A method for preparing a new composition of matter comprising mixing a copolymer containing 80 to 98 'percent of acrylonitrile and 2 to 20 percent of vinyl acetate, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of an inhibiting agent, said inhibiting agent containing substantiallyequal proportionsby weight of phenolphthalein and sulfuric acid,

and heating the mixture to a temperature in the range of 25 C. to the boiling point of the mixture to form a homogeneous solution.

16. A method for preparing a new "composition of matter comprising mixing a polymer blend of 80 to 99 per- -cent of (A) a copolymer containing 90 to-98 percent of acrylonitrile and '2 to 10 percent of vinyl acetate andl to '20 percent of (B) a copolymer containing 10 to 70 per- References Cited in the file of this patent UNITED STATES PATENTS 2,502,030 Scheiderb'auer Mar. 28, 1950 

1. A NEW COMPOSITION OF MATTER COMPRISING OF POLYMER CONTAINING AT LEAST 80 PERCENT OF POLYMERIZED ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHER POLYMERIZABLE MONO-OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENT THEREFOR, AND AN INHIBITING AGENT CONTAINING SUBSTANTIALLY EQUAL PROPORTIONS BY WEIGHT OF PHENOLPHTHALEIN AND AN INORGANIC ACID HAVING AN IONIZATION CONSTANT GREATER THAN 1X10-4. 